1. Field of the Invention
The present invention relates to a groove machining method, which forms narrow grooves on a face to be machined of a member to be machined such as a metal plate by injecting a water jet from injection nozzles of a water jet device, and also relates to a heat exchanger member and a heat exchanger.
2. Description of the Related Art
Narrow grooves have conventionally been formed on a surface of a metal plate or the like by means of various machining methods such as “groove machining method by chemical etching”, “groove machining method by water jet”, and “groove machining method by micro blasting”. A description will now be given of an overview relating to the conventional examples of the groove machining method which forms narrow grooves on a surface of a metal plate or the like. A groove machining method according to the first conventional example is a machining method which employs a photographic printing technology, protects a portion which is not to be machined with resin or the like, and then forms passages (grooves) by means of etchant.
“Groove machining method by means of water jet, and manufacture of die for forming honeycomb structure” relating to the second conventional example is a method for machining grooves with a bottom on a surface of a workpiece. More particularly, it is a method for manufacturing a die for forming a honeycomb structure, by moving a position for applying an injection to a workpiece along positions where grooves are formed at a relative speed equal to or more than 200 mm/minute, having supply holes for supplying a material, and slit grooves which communicate with the supply hole, are arranged as a grid, and form a material into a honeycomb shape, where the respective slit grooves have a depth ten or more times as long as the width (refer to Japanese Patent Laid-Open No. 2004-58206, for example).
“Chemical reactor with heat exchanger” relating to the third conventional example describes machining of passages (grooves) of a heat exchanger. Namely, it describes that “the heat exchanger of choice is one formed from a plurality of plates superposed and diffusion bonded to form a stack of plates, wherein each plate is selectively configured according to the desired pattern of channels by a chemical or mechanical treatment to remove a surface material e.g. by chemical etching, hydraulic milling, or cutting by means of water jet to a desired depth” (refer to U.S. Pat. No. 6,921,518, for example).
It is considered that the groove machining method according to the first conventional example is excellent in enabling to machine passages (grooves) in a very complex shape. However, the technology according to the first conventional example cannot form deep passages (grooves), and can form only shallow passages (grooves) whose aspect ratio (aspect ratio of the groove) is in a range of 1 to 0.5, for example. Moreover, since the etchant (corrosive liquid) is used, there poses such a problem that it is difficult to etch in metals such as aluminum whose corrosion reaction speed is high. Further, it is also necessary to dispose waste liquid, and there thus poses such an economical problem that the capital investment relating to the facility increases, resulting in a high cost.
The groove machining method according to the second conventional example manufactures a die for forming a honeycomb structure having grooves whose width and depth are respectively 0.1 mm and 2.5 mm by repeating injection of a water jet at 240 mm/minute 240 times. In other words, the groove machining method according to the second conventional example has such a problem that a very long period is required for machining, which is not practical, and, also, the movement of the injection nozzle should be repeated 240 times for the same point while injecting the water jet, resulting in difficult management of machining precision. Moreover, no description is given of machining grooves in a very complex shape.
U.S. Pat. No. 6,921,518 relating to the third conventional example includes a description that a surface material is removed down to a desired depth with chemical etching, hydraulic milling, or cutting by means of water jet.
However, the technology according to the third conventional example intends to manufacture a heat exchanger, simply describes the general methods which are considered to be able to form passages upon a thin plate, and does not describes any specific methods.
When grooves are machined on a plate, the surface area per volume increases, and if the plate is used for a heat exchanger and a reactor, a heat transfer area increases, an area contributing to a reaction increases, and the performance of the heat exchanger and the reactor thus increases. The increase of the surface area per volume by means of machining deep grooves on a plate is extremely efficient for increasing the performance of heat exchangers and reactors. Moreover, the machining of deep grooves on a plate reduces the number of plates to be machined for acquiring the same surface area, and, thus, leads to a reduction of a period required for switching the plates, a reduction of the period for the machining, and a reduction of the machining cost.
If an end of a groove is machined by means of the water jet inside an outline of a face to be machined of a member to be machined, the travel (start, stop, and velocity) and the injection (start, stop, and injection power) of an injection nozzle have conventionally been controlled. Therefore, it is difficult to maintain equal groove machining conditions at the beginning of, in the middle of, and at the end of the machining of a groove, and it is thus extremely difficult to maintain constant depth and width of the groove at a start end and a terminal end of the groove. For example, if one tries to stop the injection as soon as the travel of the injection nozzle stops, a residual pressure inside the injection nozzle does not allow to stop the injection immediately, and there poses such a problem that the water jet penetrates a member to be machined. Moreover, if the injection is gradually weakened so that the injection of the water jet is stopped (the residual pressure becomes zero) when the injection nozzle stops traveling, or the injection is caused to start as soon as the injection nozzle starts traveling, the depth and the width of a groove gradually increase or decrease, and there thus poses such a problem that constant depth and width cannot be achieved.
Due to the above various problems, it is difficult to employ the water jet for machining a groove in a complex shape, which requires control of frequent starts and stops of the travel and injection of an injection nozzle. Moreover, if a fluid is caused to flow a groove (passage) whose depth or width is not constant, the groove is blocked, or an abnormal pressure loss occurs due to a change in the cross section of the groove. As a result, since it is difficult to apply a water jet device to groove machining on a heat exchanger member (heat exchange core) where ends of grooves are formed inside outlines of faces to be machined, and the depth and the width of the grooves should be constant, it is necessary to mainly employ cutting or etching for machining the grooves on the heat exchanger member (heat exchange core).
However, since the machining of grooves by means of etching have above various problems, and a groove whose aspect ratio is equal to or more than 1, whose shape is complex and whose depth is constant cannot be machined in a short period, there has been a strong need for establishing a groove machining method which enables such a groove. With respect to the facility cost (elimination of a facility to dispose etchant) and the function to machine deep grooves, it is preferable to establish a method for machining such grooves by means of the water jet.
It is an object of the present invention to provide a groove machining method by means of a water jet which machines in a short period deep grooves whose aspect ratio is equal to or more than 1, whose shape is complex, and whose depth is constant. It is another object of the present invention to provide a heat exchanger member which has a wide surface area per volume. It is still another object of the present invention to provide a heat exchanger of high heat transfer performance by using this heat exchanger member.